1. Field of the Invention
The present invention relates to a heat exchanger suitable for use in an air conditioning system for vehicles, and more particularly to an improved heat exchanger having a pair of tanks and a plurality of heat transfer tubes interconnected therebetween.
2. Description of the Related Art
FIGS. 26 to 28 depict a conventional heat exchanger used in an air conditioning system, for example, an evaporator or a condenser. In FIGS. 26 and 27, a heat exchanger 101 includes an upper tank 102 and a lower tank 103. Upper tank 102 includes an upper wall 102a and a lower wall 102b. Lower tank 103 includes an upper wall 103a and a lower wall 103b. A plurality of heat transfer tubes 104 are fluidly interconnected between lower wall 102b of upper tank 102 and upper wall 103a of lower tank 103. Inlet pipe 105 and outlet pipe 106 are connected to upper tank 102. A heat medium, for example, refrigerant, introduced into inlet pipe 105 flows in heat exchanger 101 from inlet pipe 105 to outlet pipe 106, for example, as shown in FIG. 29. When the heat medium flows through heat transfer tubes 104, heat exchange between the heat medium and air flow 107 passing through the heat transfer tubes 104 is performed.
In such a conventional heat exchanger, however, because each tank 102, 103 is formed from a thin and flat plate (for example, aluminum plate or aluminum alloy plate), the tank walls may become deformed, as shown by the dashed lines in FIGS. 26-28, when the pressure in the tanks exceeds a certain level. Upper wall 102a of upper tank 102 and lower wall 103b of lower tank 103 are particularly likely to be deformed.
In addressing this problem, two alternative tank constructions have been proposed. The first employs relatively thicker plates, while in the second, partitions are used to connect the upper and lower walls. The former construction increases the weight and cost of the heat exchanger. The latter construction requires a complicated mold for forming a tank, and also increases the cost of the heat exchanger. Further, if too many partitions are disposed in the tank, the heat medium encounters higher fluid resistance. This reduces the efficiency of the heat exchanger.